I wish to know, if in the case of chiropractic treatment, there are
any guidelines laid down, on how long treatment (i.e. how many
treatments) should continue without any improvement in the patient's
condition, before referral should be made to another healthcare
professional e.g. the patients own GP

Are you asking about a city in the USA or world wide? My guess is
plenty of vauge guidelines, scarcely anything with teeth.   Neil

There are no "hard set" regulations but in general if a patient, under
normal conditions, shows no progress or improvement in 4-6 weeks, the
practitioner is obligated to either alter the course of treatment or
refer the patient. There are cases (some arthritides, degenerative
diseases, chronic conditions, etc...) where improvement in the
patient's condition cannot be reasonably expected or the timeline
varied. In these cases the practitioner may treat for prolonged
treatment for the purposes of "maintenance" or "wellness care" as long
as the patient is made aware of their status.

Although there is no law specifying these guidlines, the chiropractor
is by law expected to delegate a level of care comparable to what his
peers would do under simular circumstances. Therefore, were he/she to
misdiagnose, fail to diagnose, or treat the patient in a manner
inconsistent with his/her diagnosis, the (US) courts will likely find
him/her guilty of negligence.